Adhesions commonly form between an organ and surrounding connective tissue and bone after a surgical procedure. Following surgical trauma, connective tissue surrounding the organ proliferates to from a fibrous mass that binds the organ to neighboring organs, viscera, muscle, or bone. Depending on the type of surgery and the location of the incision, the adhesions may produce negligible discomfort or severe pain. However, adhesion formation can significantly complicate subsequent surgical procedures at the same or adjacent sites. Repeat surgical procedures are fairly frequent in the back, cardiac, abdomen and cranium. The presence of post-operative adhesions from a prior surgery complicates the second surgery because the contacts between the target organ and the neighboring bone and connective tissue must be carefully dissected away before the surgeon can initiate the corrective surgical procedure. The surgeon risks damaging the target organ during the dissection and the time required for the dissection procedures adds to the total time that the patient is under general anesthesia.
An unfortunate consequence of modern back surgery, whether lumbar, thoracic, or cervical surgery, is the formation of post-operative scar tissue. Scar formation surrounding the dura and nerve roots oftentimes will compress the nerve roots and cauda equina, thereby producing neural complications such as persistent low back pain, sciatica, and/or bowel and bladder dysfunction. Multiple revision operations may prove necessary due to recurrent disk herniation, post-operative spinal stenosis (iatrogenic or acquired), or because of exuberant epidural fibrosis.
Scar tissue formation after laminectomies and laminotomies for disk excision or a decompressive laminectomy for spinal stenosis present both surgeon and patient with an additional post-operative concern. Laminectomies and laminotomies frequently remove bone tissue and leave the dura exposed. Post laminectomy scar tissue, also termed epidural fibrosis, is primarily formed from fibrous connective tissue and develops in the post-operative hematoma that forms between the paraspinous muscles and the dura. The dura is relatively thin and can easily be injured during surgery. In particular, the dura is susceptible to damage during revision surgery when scar tissue adheres to the dura making it difficult for the surgeon to perform an adequate neurolysis. Thus, a method is needed for protecting the dura from scar tissue adhesion.
At the present time, methods to minimize the amount of scar tissue include the use of autogenous fat grafts, gelatin foams or sponges, or microfibullary collagen as an interposing protective layer between the spinal dura and the adjacent viscera. Other biological substances and chemical compounds that have been tested experimentally for their usefulness in animals include bone grafts, microfibrillar collagen, elastase, polyethylene, mylar, dacron, teflon and methylmethacrylate.
Autogenous fat grafts have been used following laminectomies as early as 1964. The fat is placed over the exposed dura after removal of the lamina or a portion of the lamina. The fat provides a protective barrier for the dura, and may limit scar formation between the muscle and the dural tissue. However, fat grafts are known to frequently adhere to the dura. These adhesions complicate revision surgery because they require tedious dissection by the orthopaedic or neurosurgeon. Fat grafts are preferably harvested from a sight close to the surgical incision, such as the subdermal areolar tissue bed. However, unless the patients are overweight, fat harvesting from nearby locations is not always possible, particularly in multiple laminectomy procedures. Further, fat harvesting may require a second incision. The incisions at the secondary locations may sometimes lead to complications such as hematoma formation or dimpling in the skin.
Other substances are used where fat grafts are not possible or desired. Gelatin foam (such as Gelfoam.RTM. sponge, supplied by Upjohn Company Inc., Kalamazoo, Mich.), or polylactic acid (PLA) is a useful substitute for autogenous fat grafts. This material is also placed over the dura to reduce scar formation. There is some controversy concerning the preference of gelatin foams or sponges versus fat; however, neither is optimal. Like fat, gelatin foams or sponges may move out of position following surgery. Furthermore, while fat and gelatin foams may form a barrier between the visceral tissue and the dura, there is a propensity for both fat and gelatin foam or sponge to adhere to the dura. Neither fat nor gelatin foam provides adequate physical protection to the cauda equina.
A mechanical barrier that would provide support to the spinal dura as well as reduce scar formation is needed. U.S. Pat. No. 4,013,078 to Feild discloses a device for preventing adhesions between the patient's dura and spinal nerves and other anatomic structures following spinal surgery. The device includes a conduit sheath of teflon or silicone that is positioned in close proximity to the nerve root. Like the previous protective overlay substances, such a device is invasive to the neuroforamen and anchors directly to the dura. This in turn would promote adhesions between the dura and the protecting device creating unnecessary complications for revision surgery.
In order to minimize the surgical time for dissection, minimize nerve injury and minimize dural tears a spinal cord protection device should be simple to insert, non-invasive to the dura and maintain a distance from the neural tissues. Preferably, anchoring means should contact bone instead of tissue prone to scar formation to minimize post-operative epidural fibrosis. Finally, the optimal mechanical device is readily contoured to provide a customized mechanical barrier to prevent dural or nerve root injury. Preferably, the device is adaptable in design to accommodate other surgical devices used in back surgery. Such a device is provided in the detailed description of this invention.
Adhesions also form between the heart and the anterior thoracic skeleton following cardiac surgery. In particular, adhesions form between the posterior surface of the sternum and the anterior surfaces of the heart. Repeat open heart surgeries are complicated by adhesion formation because the scar tissue must be dissected away before the sternum can be cut lengthwise and before the anterior thoracic skeleton can be retracted to expose the heart. For example, it is estimated that there are at least 250,000 coronary artery bypass graft surgeries done each year in the United States. Approximately 20% of these surgeries are revision surgeries. Adhesions form between the greater vessels of the heart and the posterior surface of the sternum. The adhesions make the separation of the pericardium from the sternum difficult and thus create severe complications during revision surgeries. It is estimated that 2 to 4% of the revision surgeries end in fatality as a result of adhesion-induced complications. Therefore, there is a need for a device that minimizes adhesion formation. The present device fulfills this need. Moreover, the device is simple to insert, easy to remove and prevents the formation of adhesions between the heart and the posterior surface of the sternum.
The present invention comprises methods and apparatus for spinal protection following spinal surgeries. In one embodiment, the invention comprises a biocompatible protection device comprising a substantially pliable shield adapted to cover a bony dissection in the spine of a vertebrate. The shield may comprise a woven metal fiber, and may include attachment ports for attaching the shield to bone such that contact between the spinal dura and the entire protection device is substantially avoided. The invention also comprises methods for spinal protection. In one embodiment the invention comprises a method of minimizing the post operative formation of adhesions to a spinal dura exposed by spinal surgery comprising the step of attaching a device comprising a substantially pliable shield to a vertebra such that the shield is positioned over the exposed spinal dura but is not in contact with the exposed spinal dura.